A public key infrastructure (PKI) is a set of hardware, software, people, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates. In cryptography, a PKI is an arrangement that binds public keys with respective user identities by means of a certificate authority (CA). The user identity must be unique within each CA domain. A third-party validation authority (VA) can provide this information on behalf of the CA. The binding is established through a registration and issuance process, which, depending on the assurance level of the binding, may be carried out by software at a CA or under human supervision. The PKI role that assures this binding is called the registration authority (RA), which ensures that the public key is bound to the individual to which the public key is assigned. PKI enables users to securely communicate on an insecure public network, and reliably verify the identity of a user via digital signatures.